The present invention relates to a cold forming method and apparatus for producing a stepped hollow component such as, for example, a gear blank.
In, for example, "Impact Machining", page 57, FIG. 3.19, Verson Co., Corona-Sha, a method is proposed which employs six press steps between the cutting of a metal bar and a final coining operation. More particularly, between the cutting and final coining operation at least two annealing steps and three lubrication treatments are required. Moreover, in the proposed method it is necessary to provide a relatively large capacity press in order to bear the heavy processing load which occurs particularly during rearward and forward extrusion steps; however, a disadvantage of the requirement for a large capacity press resides in the fact that a service life of the molds is significantly reduced by virtue of the high pressure applied to them during the press operation. Furthermore, an excessive number of steps in the proposed method tends to reduce a dimensional accuracy of the produced stepped hollow component.
The aim underlying the present invention essentially resides in providing a method and apparatus for producing stepped hollow components, which method and apparatus reduce the processing load while also reducing the number of process steps to which the hollow components must be exposed thereby increasing the overall dimensional accuracy of the produced component.
In accordance with advantageous features of the present invention, a stepped hollow article or component is attained by placing a solid slug provided with a disc portion and projecting portion in a rigid cylindrical recess, restraining an outer periphery of the disc portion and a side surface of the projectiong portion, and forming a closed-base hole in a center of the solid slug by a plastic deformation.
Advantageously, in accordance with further features of the present invention, for the purposes of restraining the outer periphery of the disc portion and side surface of the projecting portion, an annular lower surface and the side surface of the disc portion are restrained and an annular upper surface of the disc portion is precompressed so as to simultaneously restrain the side surface of the projecting portion.
In order to form the closed-base hole in the center of the solid slug, in accordance with the present invention, a press member is driven into the center of the projecting portion. Additionally, the press member may be driven to the point so as to punch out the base forming the closed hole in the center of the solid slug.
The rigid cylindrical recess may, in accordance with the present invention, be formed between a hollow mold and a counter punch, with the hollow mold accommodating the disc portion and the counter punch being adapted to fit into a lower part of a central bore of the hollow mold. Advantageously, the precompressing of the annular upper surface of the disc portion is accomplished by an outer punch fitting into the central bore in the hollow mold so as to simultaneously restrain the side surface of the projecting portion. An inner punch, fitting into a central bore of the outer punch is independently driven into the center of the projecting portion, with the plastic deformation being caused by the inner punch whereby the material of the solid slug flows biaxially in the radial and axial directions of the solid slug.
In accordance with advantageous features of the apparatus of the present invention, a first means is provided for mounting a solid slug provided with the disc portion and the projecting portion, with a second means being provided for accommodating the disc portion and the first means which is adapted to fit into the lower part of the central bore of the second means so that a recess is formed therebetween. Third means are adjustably fitted into the upper part of the central bore of the second means for precompressing an annular upper surface of the disc portion so as to restrain an outer periphery of the disc portion and the side surface of the projecting portion of the solid slug. A fourth means is fitted into a central bore of the third means and is driven independently for forming a closed base hole in a center of the projecting portion by plastic deformation which causes the material of the solid slug to flow biaxially in the radial and axial directions of the solid slug.
Advantageously, in accordance with further features of the present invention, the third means is arranged to be moved upwardly so as to absorb excessive forces caused in an axial direction of the boss portion by the plastic flow of material when the fourth means is operated.
An object of the present invention resides in providing a method and apparatus which enables the production of stepped hollow components with a high dimensional accuracy by using a minimum of processing steps in a low load by cold forming.
Another object of the present invention resides in providing a method and apparatus which relies upon a biaxial plastic flow, namely, in radial and axial directions, so as to enable a reduction in the working pressure and ensure a high precision process and article.
Another object of the present invention resides in providing a method and apparauts for producing a stepped hollow component which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
Yet another object of the present invention resides in providing a method and apparatus for producing stepped hollow components which may be readily carried out without the use of large capacity presses.
Yet another object of the present invention resides in providing a method and apparatus for producing a stepped hollow component which may be formed by a single press operation.
A still further object of the present invention resides in providing a method and apparatus for producing a stepped hollow component by cold forming which enables a marked improvement in the overall production efficiency.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, several embodiments in accordance with the present invention.